1. Field of the Invention
The present invention relates to an inductance part which is provided with a short ring, and an electronic apparatus therewith.
2. Description of the Related Art
A CPU which is mounted in an electronic apparatus such as a notebook personal computer is generally operated, using a switching-type power supply circuit such as an AC/DC converter. This power supply circuit is configured by combining an inductance part such as a choke coil, a switching device, and the like.
In recent years, an LSI such as a CPU has been processing data at higher speed, and an LSI itself has been increasingly integrated. This has also raised demands for heightening the frequency of the above described power supply circuit and increasing its electric current. Therefore, an inductance part which is mounted on the power supply circuit has also been required to supply a large quantity of electric current from several to dozens of amperes within a high-frequency range. In addition, an electronic apparatus has recently become smaller and thinner, thus demanding that an inductance part be made smaller and with a thinner profile.
As described above, if a power supply circuit is operated at a high frequency and at a large quantity of electric current, a magnetic flux leaks from an inductance part when an electric current is passed through the power supply circuit. This leakage magnetic flux may cause a peripheral circuit or apparatus, such as a CPU, to generate a high-frequency noise. As a result, operation of the circuit or apparatus may be adversely affected. This presents a demand that such a magnetic flux which leaks from an inductance part be reduced as much as possible.
Accordingly, as a conventional inductance part, for example, a coiled-wire part for a power source is disclosed, as shown in FIG. 15, in Japanese Patent Laid-Open No. 2000-82623 specification. In the coiled-wire part for a power source shown in FIG. 15, a drum core 101 is attached to a terminal stand 104. Around the drum core 101, a coiled wire 102 is wound, and a pot core 103 covers the drum core 101. In the drum core 101, an opening portion is formed which is used to pull out the coiled wire 102. A gutter is formed in the terminal stand 104, and in this gutter, a conductor 105 is placed which is shaped like a coiled wire or a loop.
In recent years, however, there has been a great demand for making the size of such a part smaller, its frequency higher, and the volume of its electric current greater. To meet this demand, the above described coiled-wire part for a power source needs to be operated at a high frequency and at a large quantity of electric current. In that case, a leakage magnetic flux cannot be sufficiently kept from increasing. This disadvantage becomes conspicuous, especially, in a thin and low inductance part whose thickness h does not balance with a setting area S (e.g., h/(S1/2)≦½). A leakage magnetic flux increases in its thickness direction, thereby having a bad influence on apparatus around it.
Aiming at reducing such a leakage magnetic flux, the conductor 105 which is shaped like a coiled wire or a loop is disposed in the gutter. However, the pot core 103 is opened, and thus, a magnetic flux leaks out in the opened part. In addition, the coil is formed by the coiled wire 102. Therefore, if the coiled-wire part is used within a high-frequency range, it is impossible to operate at a large quantity of electric current while keeping a sufficient inductance value and a low direct-current resistance value.